a) Field of the Invention
This invention relates to a molding of an ABS-based resin and also to a method for controlling the quality of the ABS-resin. More specifically, this invention is concerned with a molding of an ABS-based resin, said molding having a particular morphology, and also with a method for controlling the quality of the ABS-based resin.
The term "molding" as used herein should be interpreted in such a broad sense that it may embrace therein not only molded products but also extruded or otherwise shaped products.
This invention also pertains to the provision of the following moldings made of an ABS-based resin and having the respective quality:
(A) an ABS-based resin molding with a surface having small unevenness in gloss and a high gloss; PA1 (B) an ABS-based resin molding having small unevenness in falling weight impact strength, PA1 (C) an ABS-based resin molding having a surface of an excellent delustered appearance and small unevenness in delustering and equipped with high impact strength, and PA1 (D) an ABS-base resin molding having a surface of a uniform gloss characteristic (high gloss or delustered appearance) and of small position-dependent unevenness and equipped with high impact strength. PA1 (1) The gloss is insufficient or the surface of a molding is not uniform. With respect to the gloss characteristic, in particular, the gloss of a molding may vary depending on the position (this is called "uneven gloss") even if the molding as a whole has an excellent average gloss. As a material for moldings intended for use at positions where the moldings are visible from the outside, it has been required to improve this uneven gloss. PA1 (2) The falling weight impact strength of a molding varies depending on the position (this is called "uneven falling weight impact strength"). As an industrial material, there is a need for an improvement in uneven falling weight impact strength. PA1 (3) The delustered appearance of a molding is insufficient and moreover, there is substantial unevenness in delustering. PA1 (1) A particles having an a/b ratio not greater than 1.5, wherein a and b represent a major axis and a minor axis, respectively, and PA1 (2) B particles having an a/b ratio not smaller than 5, wherein a and b have the same meanings as defined above PA1 a. .alpha..sub.s is X.sub.1 /Y.sub.1, X.sub.1 and Y.sub.1 being the percentages of the total areas of the B particles and the A particles, respectively, at the depth of 0.5-1.5 .mu.m when the total area of all the rubber particles at the depth of 0.5-1.5 .mu.m is assumed to be 100%, and PA1 b. .alpha..sub.m is X.sub.2 /Y.sub.2, X.sub.2 and Y.sub.2 being the percentages of the total areas of B particles and A particles, respectively, at the depth of at least 200 .mu.m when the total area of all the rubber particles at the depth of at least 200 .mu.m is assumed to be 100%. PA1 (1) A particles having an a/b ratio not greater than 1.5, wherein a and b represent a major axis and a minor axis, respectively, and PA1 (2) B particles having an a/b ratio not smaller than 5, wherein a and b have the same meanings as defined above
b) Description of the Related Art
ABS-based resin moldings have been employed widely as moldings for engineering and like applications, such as parts or components for electric appliances, electronic equipments, automotive vehicles and the like, for their excellent mechanical strength, heat resistance, chemical resistance, anti-torque strength upon tightening a screw, color tone, surface appearance and the like.
ABS resin is required to be available as polymers with properties varied to meet application purposes. Polymers even with totally opposite properties may be needed, for example, to provide moldings ranging from those having a high gloss to those delustered. It is also required to achieve various and stringent properties to assure, for example, high impact strength and prevention of position-dependent unevenness in gloss, delustered appearance and impact strength of moldings.
To achieve these, it is generally necessary to control physical properties by choosing or adjusting rather complex conditions such as the kind of a rubber component to be graft polymerized, its particle size and conditions for the graft polymerization. Under the current circumstances, however, it is still difficult to achieve high physical properties even if such conditions are chosen or adjusted as appropriately as possible.
These moldings are accompanied by various quality problems, because in the course of production of the moldings, it is difficult to mold and/or process the whole moldings under uniform conditions. Described specifically, the following problems can be mentioned:
This uneven gloss will be described in further detail by taking by way of example a molding obtained by an injection molding machine. When a surface is formed in the course of injection molding, a gradient is developed in molding pressure between a position called a "gate portion", through which a molten polymer is fed into a mold, or its vicinity and each position located apart from the gate portion (namely, the end of each flow of the molten polymer through the mold) so that the resultant molding generally tends to have a lower gloss at end portions thereof.
Further, a practical molding has a very complex shape because of the provision of ribs or bosses for the retention of strength, mold-releasing jutting pins, and/or concave or convex portions for connection with other parts. The surface gloss of the molding therefore varies significantly depending on the position and is not uniform. Even if the molding as a whole has an excellent average gloss or a superb delustered appearance, its gloss or delustered appearance is not even locally so that the commercial value of a final product making use of the molding, for example, an electric appliance or the like is lowered.
Many methods have been proposed for improving the average surface gloss of an ABS-based resin molding. For resin compositions which comprise a rubber-modified styrene, methods for improving the balance between the average gloss value and the impact strength in each resin composition by blending, for example, a resin containing rubber particles of different particle sizes are disclosed inter alia in Japanese Patent Publication No. 41467/1971, Japanese Patent Laid-Open Nos. 1519/1984 and 241053/1988, and U.S. Pat. No. 4,146,589.
Japanese Patent Publication No. 41467/1971 referred to above discloses on page 1, right column, lines 27-31 a method for improving the balance between the average gloss value and the impact strength by blending a resin containing rubber particles of different particles, that is, rubber particles having a particle size of 0.05-0.5 .mu.m and rubber particles having a particle size of 2-10 .mu.m. This publication therefore discloses that incorporation of particles of different sizes is effective for the improvement of impact strength. No effective proposal is however made therein with respect to the theme that uneven gloss be reduced.
It has heretofore been attempted to eliminate such unevenness in gloss by devising molding conditions for the production of a molding or by modifying the design of a mold.
In recent years, there is an increasing demand for moldings with a delustered surface in the fields of interior components or parts for automotive vehicles, components or parts for home electric equipments and appliances, etc. Illustrative known methods which are commonly employed for delustering the surfaces of moldings include, as methods applied upon molding, the method in which gaining is applied to the surface of a mold and the method in which a liquid delustering agent is coated on the surface of a molding. These methods however require a special mold or a special operation. Also known is the method in which an inorganic filler such as talc, calcium carbonate or silica gel is added. To make the delustered surface appearance uniform, this method however requires the addition of the inorganic filler in a large quantity. However, this leads to a significant reduction in the impact strength and is not preferred.
To reduce such unevenness in gloss or delustered appearance, it has heretofore been the practice to cope with the problem by devising the molding conditions for a molding or devising the design of a mold on the basis of experience as described above. This approach however requires a substantial time and cost and in the case of the modification to the design of the molding, for example, the gloss may not be balanced with the strength and structure in many instances even if the unevenness gloss can be reduced as a consequence.
As methods for modifying a resin, blending methods are known. For example, Japanese Patent Laid-Open No. 142259/1979, Japanese Patent Publication No. 59725/1987, and the like can be mentioned in this respect. It is however impossible for these methods to eliminate uneven delustering without lowering other physical properties. Further, these blending methods cannot provide moldings of such a morphology as will be described subsequently herein.
It is known for many years that upon molding a resin, rubber particles are each deformed into an elliptical shape due to a stress developed inside the resin. Such a shape can be observed by electron microscope. This is disclosed, for example, in (1) "ABS Resin", Volume 1, Chapter 3: Properties of ABS Resin, page 126 (1970), Compiled by Kobunshi Kikai Zairyo Iinkai and (2) "Plastic Age", Volume 39, January, 139 (1993).
No study has however been made on the control of physical properties of a molding by relying upon the morphology of such rubber particles. In the molding disclosed in the above publication (1), all rubber particles have been similarly deformed in a somewhat flattened shape. In the molding disclosed in the above publication (2), rubber particles located within a certain distance from its surface have all been subjected to considerable deformation. In these conventional examples, the rubber particles have been deformed almost uniformly near the surface.
Uneven falling weight impact strength will next be described in detail, for example, in connection with a molding obtained by an injection molding machine. Upon formation of a surface by injection molding, the resin undergoes orientation. The resin is strongly oriented especially at each position in a mold, where the molten resin moved at a high flow rate. The falling weight impact strength of the portion so oriented tends to become lower compared with a portion corresponding to a position in the mold, where the molten resin moved at a low flow rate. In the case of a planar molding, for example, the falling weight impact strength tends to become lower as the point of measurement becomes closer to the position corresponding to a gate because the molten resin in the mold has a higher flow rate in the vicinity of the gate portion. Further, a practical molding has a very complex shape because of the provision of ribs or bosses for the retention of strength, mold-releasing jutting pins, and/or concave or convex portion for connection with other parts. Surface molding conditions of the molding therefore vary considerably depending on the position and moreover, the strength varies substantially. Even if a resin having, for example, a high Izod impact strength test value is used, the uneven falling weight impact strength formed upon molding and the existence of local portions having smaller strength cause problems. To increase the strength of such local portions, a measure has heretofore been taken to increase the content of a polycarbonate in the resulting resin where an ABS resin is blended with the polycarbonate. Many methods have heretofore been proposed to improve the average impact strength or an average falling weight strength. No effective method is, however, proposed for the elimination of the falling weight impact strength of the present invention.
With a view toward eliminating such uneven falling weight impact strength, certain measures have been taken including devising of molding conditions and modifications to the design of a mold and in the case of such a blend system as described above, blending of an expensive resin of high strength in a greater percentage. These methods are however difficult to overcome the above problem, because they require a substantial cost and in the case of the modification of the design of the mold, for example, the average gloss and the impact strength can hardly be balanced in many instances.